Search for: All records

Understanding of fission properties of super-heavy nuclei (SHN) is essential not only for the synthesis of new elements but also for astrophysical nucleosynthesis because fission fragments from SHN are recycled as the seed nuclei of the r-process. A recent discovery of the r-process site by the gravitational wave observations requires more precise nuclear information for the detailed simulation of the r-process nucleosynthesis. However, the fission mechanisms of the SHN are not understood well, and therefore theoretical predictions of distributions of the fission fragments of SHN are very model-dependent. Our four-dimensional Langevin model can calculate various properties of the fission fragments, such as the distribution of fission yields, kinetic energies, and deformation of fission fragments and their correlations just after scission. Those results are consistent with the experimental data, especially in the actinide region without adjusting parameters. Based on such a reliable model, we previously investigated the fission of representative SHN where the experimental data exist and found that doubly-magic shell closure of 132 Sn and 208 Pb dominates the fission process. This paper demonstrates the results of our calculations for the systematics of fission yield and the total kinetic energies from the neutron-rich to the neutron-deficient side of SHN. We also show decomposition of fission modes, such as standard/super-long/super-short modes, based on a Brosa-like concept. 

We studied the fission barrier of 236 U with a microscopic mean-field model employing Skyrme-type effective interaction. It has been known that the microscopic mean-field calculation had a trend of overestimating the fission barriers derived from the fission cross section, and our results were found to be in accord with it. To reveal a major factor of the discrepancy, we investigated various components of the Skyrme energy-density functional building of the fission barrier height by a static mean-field model, including nuclear pairing correlation. We found that the spin-orbit and pairing terms affected the fine structure of the fission barrier as a function of elongation of the nucleus. Therefore, we investigated the sensitivity of the fission barrier height on the pairing strength, considering the change of level density along the calculated fission path. 

The distribution of the spin-dipole strengths in 16 O and neutrino-induced reactions on 16 O areinvestigated by shell-model calculations with new shell-model Hamiltonians. Chargedcurrent and neutral-current reactioncross sections are valuated in various particle and γ emission channels as well as the total ones at neutrinoenergies up to Eν≈ 100 MeV. Effects of multiparticle emission channels, especially the αp emission channels, on nucleosynthesis of 11 B and 11 C in core-collapse supernova explosions are investigated. The MSW neutrino oscillation effects oncharged-current reaction cross sections are investigated for future supernova burst. Electron capture rates for a forbidden transition 20 Ne(O g.s. + ) → 20 F(2 g.s. + ) in stellar environments are evaluated by the multipole expansion method with the use of shell model Hamiltonians, and compared with those obtained by a prescription that treats the transition as an allowed GamowTeller (GT) transition. Different electron energy dependence of the transition strengths between the two methods is found to lead to sizable differences in the weak rates of the two methods.